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Photosynthetic pathway,chilling tolerance and cell sap osmotic potential values of grasses along an altitudinal gradient in Papua New Guinea
Authors:M. J. Earnshaw  K. A. Carver  T. C. Gunn  K. Kerenga  V. Harvey  H. Griffiths  M. S. J. Broadmeadow
Affiliation:(1) Department of Cell and Structural Biology, University of Manchester, Williamson Building, M13 9PL Manchester, UK;(2) Biology Department, Oakham School, Oakham, LE15 6DT Rutland, Leicestershire, UK;(3) Division of Botany, Department of Primary Industry, Office of Forests, P.O. Box 314, Lae, Papua New Guinea;(4) Department of Biology, The University, NE1 7RU Newcastle upon Tyne, UK
Abstract:Summary A total of 22 grass species were examined from 5 sites spanning the altitudinal range 1550–4350 m.a.s.l. The presence of the C3 or C4 photosynthetic pathway was determined from delta13C values and chilling tolerance was assessed on the basis of electrolyte leakage from leaf slices incubated on melting ice. Most of the grasses studied at the lower altitude sites of 1550 m.a.s.l. (annual mean of daily minimum temperature, 14.6° C) and 2600 m.a.s.l. (9.4° C) possessed C4 photosynthesis and were chill-sensitive. The single except ion was Agrostis avenacea, a montane chill-resistant C3 species which occurred at 2600 m.a.s.l. The three species apparently most sensitive to chilling were Ischaemum polystachyum, Paspalum conjugatum and Saccharum robustum, all occurring at 1550 m.a.s.l. At the higher altitude sites of 3280 (5.6° C), 3580 (4.0° C) and 4350 (–0.7°C) m.a.s.l., most of the grasses exhibited C3 photosynthesis and were chill-resistant. However, an Upland population of the C4 species, Miscanthus floridulus was found at 3280 m.a.s.l. which had acquired chill-resistance as confirmed by additional in vivo variable chlorophyll fluorescence measurements. Cell sap osmotic potential values of the upland grasses at altitudes of 3280–4350 m.a.s.l. were lower (–8.1 to –19.8 bars) than values in grasses from 1550 and 2600 m.a.s.l. (–3.9 to –7.5 bars) due mainly to the presence of non-electrolyte osmoticants, which may be involved in frost avoidance mechanism(s).Abbreviations ABA abscisic acid - FR the maximal rate of rise of induced chlorophyll fluorescence - psgrs osmotic potential
Keywords:Altitude  C3/C4 photosynthesis  Chilling tolerance  Frost hardiness  Tropical habitat
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